Method for forming patterned films using a flexographic apparatus having a temperature control device embedded in a substrate support

ABSTRACT

A flexographic apparatus including a plate having a relief pattern for printing on a substrate to be printed is provided with a temperature control, preferably embedded within a stage for supporting the substrate to be printed. The substrate to be printed may be controlled at a temperature above 30° C.

This application is a division of application Ser. No. 07/899,366, filedJun. 16, 1992 now U.S. Pat No. 5,279,858.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a flexographic apparatus having atemperature control means for keeping a substrate to be printed at aconstant temperature and a method of forming a film of an organicpolymer or an inorganic oxide thereby.

A conventional flexographic apparatus roughly has an arrangement, asshown in FIG. 3, including a stage 1 to which a substrate (to beprinted) 11 is fixed, a cylinder 2, a relief plate 3 having a printingpattern and fastened to the cylinder 2, an extension plate 8, a nozzle 5for supplying to the extension plate 8 a printing liquid 4 fed from atank 6, and a doctor blade 7 for extending or spreading the printingliquid on the extension plate 8. A commercially available example ofsuch a flexographic apparatus is "Angstromer" (trade name, availablefrom Nihon Shashin Insatsu K.K.).

However, when an organic polymer solution or an inorganic oxide solutionis applied on a substrate by using a conventional flexographic apparatusas described above, the resultant organic polymer or inorganic oxidefilm is sometimes accompanied with a nonuniform thickness distributionor poor smoothness (undulation), which results in adverse effects to theproperties of the film.

SUMMARY OF THE INVENTION

In view of the above-mentioned problem of a conventional flexographicapparatus, an object of the present invention is to provide aflexographic apparatus and a film-forming method using the apparatus,whereby a liquid containing an organic polymer, an inorganic oxideprecursor, etc., may be applied to provide a film with an improveduniformity of thickness distribution, an improved smoothness and animproved reproducibility of these factors.

According to the present invention, there is provided a flexographicapparatus, comprising a plate having a prescribed relief pattern forprinting on a substrate to be printed, and a temperature control meansfor controlling the substrate at a temperature above 30° C.

According to another aspect of the present invention, there is provideda flexographic apparatus, comprising a plate having a prescribed reliefpattern for printing on a substrate to be printed, a stage forsupporting the substrate to be printed, and a temperature control meansembedded within the stage.

According to a further aspect of the present invention, there isprovided a method for forming an organic polymer film, comprisingapplying a solution of the organic polymer onto a substrate to beprinted by a flexographic apparatus while controlling the substrate tobe printed at a temperature above 30° C.

According to a further aspect of the present invention, there isprovided a method for forming an inorganic oxide film, comprisingapplying a solution of an inorganic oxide precursor onto a substrate tobe printed by a flexographic apparatus while controlling the substrateto be printed at a temperature above 30° C.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view showing an outline of a flexographic apparatusaccording to the present invention.

FIG. 2 is a plan view showing a stage supporting a substrate to beprinted used in the apparatus shown in FIG. 1.

FIG. 3 is a front view showing a conventional flexographic apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The temperature control means used in the present invention may forexample be embodied as a temperature control mechanism for keeping at aconstant temperature a stage for supporting or fastening a substrate tobe printed in a flexographic apparatus.

In a preferred embodiment, a liquid, preferably a solution, containingan organic polymer or an inorganic oxide precursor may be applied onto asubstrate to be printed which is supported on the stage and controlledat a temperature above 30° C. within an accuracy of ±5° C., therebyforming a film of such an organic polymer or inorganic oxide.

Examples of such an organic polymer film may include: color filterscomprising colored resins of, e.g., polyamides, and protective filmsthereon; films of photoresists, such as photosensitive phenol-novolakresin; alignment films for liquid crystal devices, comprising, e.g.,polyimide resins; and sealants for liquid crystal devices, comprisinge.g., epoxy-type adhesives. Further, the inorganic oxide film thusformed may for example be an insulating film for liquid crystal devices.

A conventional flexographic apparatus is not equipped with a temperaturecontrol mechanism so that the temperature of the substrate to be printedis affected by the environment. In other words, the flexographicprinting has been possible only in the neighborhood of room temperature.In case where a solution of an organic polymer or an inorganic oxideprecursor is applied by flexography under such a condition, theresultant organic polymer or inorganic oxide film is liable to beaccompanied with an ununiformity of thickness distribution and/orsurface undulation, which results in adverse effects to the finalproperties of the film. According to the present invention, a solutionof an organic polymer or an inorganic oxide precursor is applied to asubstrate to be printed while the substrate to be printed istemperature-controlled at a constant temperature above 30° C. within anaccuracy of ±5° C. by equipping a flexographic apparatus with atemperature control means for keeping a stage for supporting thesubstrate at a constant temperature, so that the resultant film isprovided with improved uniformity of film thickness, surface flatnessand reproducibility thereof.

Hereinbelow, some embodiments of the present invention will be describedwith reference to the drawings.

FIGS. 1 and 2 illustrate principal features of an embodiment of theflexographic apparatus according to the present invention. Theflexographic apparatus includes a stage 1 for supporting a substrate tobe printed 11, a cylinder 2, a plate (rubber relief plate) 3 having aprinting pattern, a supply nozzle 5 for supplying a printing liquid 4supplied from a tank 6, an extension plate 8, and a doctor blade 7 forextending the printing liquid 4 on the extension plate 8.

EXAMPLE 1

In a specific example, the stage 1 was formed of a metal (e.g.,stainless steel) having a smoothened surface, and the surfacetemperature thereof was controlled at a temperature of 20°-50° C. withinan accuracy of ±1.0° C. by circulating a constant-temperature watercontrolled at a temperature of 20°-50° C.±0.5° C. within the stage 1along a circulating path 10. Correspondingly, a substrate 11 fastened toand in intimate contact with the stage 1 by vacuum generated in vacuumgrooves 13 leading to a vacuum pump was heated by conduction to atemperature of 20°-50° C.±2.0° C. within ten and several seconds.Generally, the substrate-to-be-printed should preferably be controlledwithin an accuracy of ±5° C., particularly ±3° C., according tomeasurement at, e.g., 9 points of the substrate by CA thermocouplesdirectly applied to the substrate.

On the above-mentioned stage controlled at five constant temperatures of20° C., 30° C., 35° C., 40° C. and 50° C., respectively, several glassplates (each measuring 300 mm×320 mm×1.1 mm-t) were successively placed,and a color filter ink containing a color filter resin comprising aphotosensitive polyamide resin colored with a red colorant dispersedtherein ("PA-1012R" (trade name), available from Ube Kosan K. K.)diluted to a viscosity of 500 centipoise with N-methylpyrrolidone(solvent) and extended on the extension plate 8 of SUS (stainless steel)having 36 μm-deep grooves (a groove widths of 27 μm and a convexityspacing of 25 μm between grooves, was applied onto the glass plates by aplate of a rubber ("CYREL" (trade name) available from E. I. Du Pont)having a rectangular relief pattern of 280 mm×300 mm under a plateimpression of 0.15 mm.

The color filter films printed on the glass substrates at varioustemperatures showed properties as shown in the following Table 1.

                  TABLE 1                                                         ______________________________________                                               Substrate                     Temp.                                    Sample temp.    Thickness    Undulation                                                                            range                                    ______________________________________                                        No. 1  20° C.                                                                          7650 ± 530 Å                                                                        410 Å/8 mm                                                                        ±2° C.                         No. 2  30° C.                                                                          7930 ± 510 Å                                                                        390 Å/8 mm                                                                        ±2° C.                         No. 3  35° C.                                                                          8320 ± 310 Å                                                                        180 Å/8 mm                                                                        ±2° C.                         No. 4  40° C.                                                                          8500 ± 230 Å                                                                        160 Å/8 mm                                                                        ±2° C.                         No. 5  50° C.                                                                          9380 ± 430 Å                                                                        190 Å/8 mm                                                                        ±2° C.                         ______________________________________                                    

The thickness and the undulation of each film sample were measured atseveral points and pairs of 8 mm-distant points for each of the severalpoints, respectively, by partly peeling the film in a width of 8 mm atthe several points and measuring the thicknesses of the sides of theremaining films by a contacting needle-type surface roughness meter("Surfcoder ET-30" (trade name) available from Kosaka Kenkyuso K.K.).

As is understood from the above Table 1, Sample Nos. 1 and 2 printed at20°-30° C. provided a fluctuation in thickness exceeding ±7% andundulations of 390 Å or larger. In contrast thereto, Sample No. 3printed at 35° C. provided a remarkably smaller fluctuation in thicknessof within ±4% and a smaller undulation of 180 Å or less, and Sample No.4 printed at 40° C. provided a fluctuation of within ±3% and anundulation of 160 Å or less. Sample No. 5 printed at 50° C. gave athickness fluctuation of ±5% and an undulation of 190 Å which were notinferior to the results of Samples Nos. 3 and 4. However, Sample No. 5showed some dryness due to evaporation of the solvent in the ink duringthe printing as the printing was continued on a large number of glassplates, and gradually provided inferior films.

The above results are considered to show that an elevated temperatureexceeding 30° C. of the substrate promoted leveling of the printingliquid applied on the substrate but an excessively high temperaturecaused too high a drying speed, thus being liable to provide inferiorfilm properties. However, the latter difficulty can be alleviated byusing a solvent having a higher boiling point, while a temperature up to50° C. is generally preferred.

As is understood from the above results, by using the above-mentionedflexographic apparatus to control the substrate to be printed at aconstant temperature, a color filter film having a good thicknessdistributions and good surface roughness was formed on the glass plates.

Then, each color filter film was exposed through a photomask toultraviolet rays at an intensity of 300 mJ/cm² to photocure theprescribed parts of the film, which was then developed with a prescribeddeveloper liquid to remove the uncured part of the film by dissolutionand then subjected to further curing in a clean oven at 200° C. for 1hour to form a good red color filter pattern on the glass plate.

EXAMPLE 2

Similarly as in Example 1, on the above-mentioned stage controlled atfive constant temperature of 20° C., 30° C., 35° C., 40° C. and 50° C.,respectively, several glass plates (each measuring 300 mm×320 mm×1.1mm-t) were successively placed, and a solution of a transparentpolyamide resin ("PA-1000C" (trade name) available from Ube Kosan K.K.)which may be used to form, e.g., a protective film on a color filter,diluted to a viscosity of 500 centipoise with a mixture solvent ofN-methylpyrrolidone/n-butylcellosolve and extended on the extensionplate 8 of SUS having 30 μm-deep groove (a groove width of 275 μm and aconvexity spacing of 25 μm between grooves), was applied onto the glassplates by a plate of EPT (ethylene-propylene terpolymer) having arectangular relief pattern of 280 mm×300 μm under a plate impression of0.15 mm.

The clear films printed on the glass substrates at various temperaturesshowed properties as shown in the following Table 2.

                  TABLE 2                                                         ______________________________________                                               Substrate                     Temp.                                    Sample temp.    Thickness    Undulation                                                                            range                                    ______________________________________                                        No. 1  20° C.                                                                          10220 ± 400 Å                                                                       390 Å/8 mm                                                                        ±2° C.                         No. 2  30° C.                                                                          10700 ± 250 Å                                                                       290 Å/8 mm                                                                        ±2° C.                         No. 3  35° C.                                                                          11030 ± 190 Å                                                                       160 Å/8 mm                                                                        ±2° C.                         No. 4  40° C.                                                                          11200 ± 160 Å                                                                       150 Å/8 mm                                                                        ±2° C.                         No. 5  50° C.                                                                          12320 ± 230 Å                                                                       220 Å/8 mm                                                                        ±2° C.                         ______________________________________                                    

As is understood from the above Table 2, Sample Nos. 3, 4 and 5 printedat 35°-50° C. provided fluctuations in thickness of within ±1.5-2.0% andundulations of 150-220 Å or smaller. In contrast thereto, Sample No. 1printed at 20° C. showed inferior thickness distribution and smoothness(undulation) presumably because of insufficient leveling of the ink onthe substrate. Further, Sample No. 2 printed at 30° C. showed athickness distribution and a smoothness (undulation) which were betterthan those of Sample No. 1 but inferior to those of Samples Nos. 3-5printed at 35°-50° C.

As the organic polymer material applicable in the present invention, itis also possible to use polyimides which may be used for formingalignment films principally used in liquid crystal devices,phenol-novolak resins having photosensitivity, high-temperature curableepoxy-type sealants for, e.g., liquid crystal devices. It is alsopossible to use, for application, a solution of an inorganic oxideprecursor, examples of which may include hydroxides and organo-oxides ofmetals or metalloids such as silicon, titanium, tantalum, and zirconium.These inorganic oxide precursors may, for example, be heated after theprinting to form a (patterned) film which may be used as an insulatingfilm, a protective film, or a spacer member. It has been confirmed thatthe effect of temperature control of the substrate to be printed at atemperature above 30° C. is effective for forming a film having auniform thickness and an improved flatness (less undulation) also ofthese materials.

As described above, by equipping a stage for supporting a substrate tobe printed of a flexographic apparatus with a temperature control means,the substrate can be controlled at a temperature exceeding 30° C.,preferably by 3° C. or more, within an accuracy of ±5° C., preferably±3° C., further preferably ±2° C., whereby an organic polymer film or aninorganic oxide film can be stably formed at an improved thicknessuniformity and a better flatness and with a good reproducibility byapplication of a solution of the organic polymer or an inorganic oxideprecursor.

What is claimed is:
 1. A method for making a color filter, comprisingthe steps of:measuring a temperature of a substrate by a plurality ofthermocouples directly applied to plural points of the substrate;forming a colored organic polymer film on the substrate by applying asolution comprising a polyamide resin and a colorant onto the substrateusing a flexographic apparatus comprising a cylinder and a plate held onsaid cylinder, said plate having a relief pattern for printing on thesubstrate, said flexographic apparatus further comprising a stage forsupporting the substrate, a rectangular groove formed within the stageadapted to provide a vacuum therein and secure the substrate to thestage, and a temperature control means embedded within the stage forcontrolling the substrate at a prescribed temperature from 30°-50° C.,said temperature control means including a path for circulating liquidhaving a controlled temperature, whereinsaid organic polymer solution isapplied onto the substrate while the substrate is controlled within theprescribed temperature.
 2. A method for making a color filter,comprising the steps of:selecting a substrate with a color filter layer;measuring a temperature of said substrate by a plurality ofthermocouples directly applied to plural points of the substrate;forming an organic polymer film on the substrate by applying a solutioncomprising a photosensitive phenol-novolak resin onto the substrateusing a flexographic apparatus comprising a cylinder and a plate held onsaid cylinder, said plate having a relief pattern for printing on thesubstrate, said flexographic apparatus further comprising a stage forsupporting the substrate, a rectangular groove formed within the stageadapted to provide a vacuum therein and secure the substrate to thestage, and a temperature control means embedded within the stage forcontrolling the substrate at a prescribed temperature from 30°-50° C.,said temperature control means including a path for circulating liquidhaving a controlled temperature, whereinsaid organic polymer solution isapplied onto the substrate while the substrate is controlled within theprescribed temperature.